Separator for batteries

ABSTRACT

A separator which is permeable to hydroxide ion, and which contains at least one Dendrite Stopping Substance such as Ni(OH) 2 , or its precursor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 15/122,800 filedAug. 31, 2016, which was a national stage application, filed under 35U.S.C. § 371, of International Patent Application No. PCT/IB2015/051471filed Feb. 27, 2015, which claims priority to provisional applicationNo. 61/947,327 filed Mar. 3, 2014. Each of the previously notedapplications is hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present application relates to separators for use in zinc secondaryalkaline batteries and method for manufacturing the same. Moreover thepresent invention relates to separators permeable to hydroxide ion, foruse in an electrically rechargeable electrochemical cell with Zincelectrode and alkaline electrolyte, and a battery comprising saidseparator.

BACKGROUND OF THE INVENTION

It is well known that during the electrical charging of a zinc anodealkaline battery, zinc dendrites are formed, leading to the perforationof the separator that lays between the zinc anode and the chargingelectrode compartments, and therefore to a short-circuit, rendering thebattery completely useless.

The typical solution is to use a rayon type or polymeric porousseparator (e.g. anionic exchange membrane, polymeric film made byzirconia/polysulfone, polymeric films, cellulose films, etc.). Othertypical solutions of separators are described in the paper “BatterySeparators” from Pankaj Arora and Zhengming (John) Zhang published inChemical Reviews, 2004, Vol. 104, No. 10, pages 4419-4462, hereinincorporated by reference in its entirety.

However these separators are not totally satisfactory because they aretoo permeable to zincate ions and zinc dendrites are still formed andusually perforate the separator in less than 50 cycles.

One aim of the present patent application is to provide a solution toimprove the characteristics of such separators and extend their servicelife.

Another aim of the invention is to provide a separator that can greatlyenhance its ability to prevent dendrites perforation.

The invention relates to a separator which is permeable to hydroxideion, for use in an electrically rechargeable electrochemical cell withalkaline electrolyte between a Zinc electrode and a counter electrode,wherein:

-   -   said separator containing at least one Dendrite Stopping        Substance or DSS, said DSS being a metal-containing compound        such as oxide, hydroxide, salt, etc . . . , said metal chosen        from the metals of the group consisting of Pt, Pd, Ni, Fe and        Mn, and    -   said DSS being in a form of particles.

The inventor noticed that incorporating some “Dendrite StoppingSubstance” (DSS) particles in the separator's material or pores reducesdendrite formation.

In the invention “particle” means an aggregate of material whose size isbelow 500 μm.

The separator of the invention is such that during charging, i.e. whenhydroxide ions are flowing from the zinc electrode towards the counterelectrode, the dendrites growing from the Zinc electrode towards thecounter electrode are stopped in their progression through the separatorwhen they encounter DSS particles of the said separator.

Separators according to the invention can be prepared by including DSSparticles within the material of the separator when it is formed. Inother words, the DSS particles are added to the commonly used materialsthat are used to prepare separators.

Separators according to the invention can also be prepared byimpregnating, with DSS particles, porous or fibrous typical materialthat are used to form separators. Classical alkaline-stable separators(known in the art) are for instance made of Polypropylene (PP)/Polyvinylchloride (PVC), or Polytetrafluoroethylene (PTFE) or mixtures thereof.An alkaline-stable microporous separator according to the invention canbe a microporous PVC separator for use in lead-acid batteries having a45% to 70% volumetric porosity, a 0.05 μm to 10 μm pore size and a 0.1to 1 mm thickness. The above-mentioned separator that contains the DSSparticles can be obtained, for example, by soaking a classical separatorwith a DSS precursor, which results in DSS particles precipitation.

In an advantageous embodiment, the invention relates to the separatormentioned above, wherein said DSS is Ni(OH)₂ or one of its precursor,such as NiCO₃ or NiSO₄. In another embodiment, the invention relates tothe separator mentioned above, wherein the size of the DSS particles isbelow 250 μm whereby minimizing the cost of the DSS material. It is tobe noticed that larger particles would use more material and be moreexpensive for achieving the same effect.

In another advantageous embodiment, the invention relates to theseparator mentioned above, wherein the thickness of the separator isranging from 50 to 1000 μm whereby the dendrite stopping effect remains.A thicker separator would increase internal resistivity, would use morematerial and would be more expensive, while a thinner separator wouldhave less effect to stop dendrites.

The invention also relates to an electrically rechargeable battery, withstrong alkaline electrolyte, comprising at least one separator accordingto the invention, as mentioned above, said separator being placedbetween a Zinc electrode and a counter electrode.

In the invention a “strong alkaline electrolyte” means an electrolytehaving a pH of at least 12.

In some embodiments the above mentioned battery comprises, as a cathode,an air electrode.

Moreover, in some embodiments the above mentioned battery comprises, ascathode, a nickel-oxide or a silver electrode.

The present invention provides separators that are comparatively moreresistant to dendrites perforation and provides battery with longerservice life than the one not comprising DSS particles.

This invention is advantageously suitable for zinc-nickel, zinc-silver,zinc-air, lithium-air electrically rechargeable batteries, especiallyfor their use in stationery applications or electric vehicles such ase-cars, e-autobuses, e-trucks, e-bicycles, etc. Thus, the invention alsorelates to an electric or hybrid vehicle comprising at least oneelectrically rechargeable battery as mentioned above.

Another aspect of the invention relates to a method for preparing aseparator as defined above, comprising:

-   -   a step of soaking a porous or fibrous material with a DSS        precursor, such as NiCO₃ or NiSO₄ and    -   a step of having DSS particles precipitate within the said        material.

According to this process, separator commonly used for batteries issoaked into a DSS precursor. The DSS material then precipitates onto thecavities or the pores of the porous or fibrous material, conferring tothe resulting material Dendrite Stopping properties.

Another aspect of the invention relates to a method for manufacturing aseparator having Dendrite Stopping properties as defined above,comprising a step of adding DSS particles into the mixture of materialused to prepare a separator

This process allows to manufacture a separator that directly containsDSS particles, and exhibits Dendrite Stopping properties.

When preparing such a separator, it is ready to use and does not need tobe soaked with a DSS precursor.

The invention also relates to the use of a separator as mentioned above,for manufacturing an electric battery. The invention will be furtherunderstood from the following detailed description of specificembodiments. The product and method of the invention are illustrated butnot limited to the following examples.

LEGEND TO THE FIGURE

FIG. 1 shows a cross section view of a zinc-air battery cell with secondreversible electrode and without auxiliary electrode, where (11) is anair electrode; (12) is a first reversible zinc electrode; (13) is asecond reversible nickel-oxide electrode; (14) (15) are separatorsplaced in between the neighboring electrodes; (16) is the casing of thebattery.

EXAMPLES Example 1

In this first example the inventors prepare a separator according to theinvention by:

-   -   adding 7 g of 50-100 μm Ni(OH)₂ particles to 100 ml ethanol        C₂H₅OH and mixing with a magnetic stirrer 20 min.    -   then 3.3 ml of PTFE suspension (DuPont™ Teflon® PTFE TE-3893        with particle size 0.05 to 0.5 μm, solid content 60%, density        1.5 g/cc) is added to the mixture and further mixed for 2 h.    -   then the mixture is left to rest and decant.    -   then the decanted solid mass is well kneaded and rolled 12 times        to obtain separator layers of thickness down to 0.2 mm.    -   finally, these separator layers are dried 48 h at 30° C. during        which time the thickness of the separator increases from 0.2 mm        up to 0.25 to 0.3 mm.

The separator obtained has a very good dendrite stopping effect.

It is to be noted that by using Ni(OH)₂ particles smaller than 50 μmthinner layers can be rolled, thus permitting to obtain a separatorfinal thickness of only 0.1 to 0.15 mm.

Example 2

In this second example to prepare a separator according to theinvention, the inventors use a microporous PVC separator having athickness of 1.1 mm for use in lead-acid batteries manufactured byMicrotex Energy P Ltd., Bengaluru-560058, Karnataka, India. Thismaterial is first soaked during 1 hour with a 200 g/l NiSO₄ solution(nickel sulfate NiSO₄ is very soluble in water), then impregnated during1 hour by strong alkaline solution, 100 g/l KOH, resulting in aprecipitation of Ni(OH)₂ particles within the pores of the microporousseparator. It is to be noted that Ni(NO3)2 and NiCl2 could be usedinstead of NiSO₄ as DSS precursor, while NaOH, Na₂CO₃ or K2CO3 could beswapped for KOH. Also the concentrations of both the DSS precursor andalkaline electrolyte can vary in a range of 35% to 300%.

Then the separator is well rinsed in water and dried, the excess ofNi(OH)₂ being removed from the separator's surface mechanically.

As a result, the in-pore Ni(OH)₂ particles could occupy from 5 to 50% ofpore volume with various particle-size distribution.

Ni(OH)₂ particles are 5 to 10 weight percent from the final separator'sweight.

Such prepared separator possesses enhanced counter-dendrites properties.

Example 3

In this third example one cell zinc-air battery is prepared including:

1—a Zinc anode, an Air-Electrode and an auxiliary electrode as describedin FIG. 2 of WO2013/110097. Briefly, the battery cell contains thecomponents described below with an additional indifferent auxiliaryelectrode made of fine nickel mesh (such as 6 Tyler mesh), it could alsobe an Ni-coated iron grid, electrically connected to the nickel-oxideelectrode during cell charge.

A battery cell is prepared, and as shown in FIG. 1 contains thefollowing components:

-   -   an air electrode (11) produced by the company MEET (Korea,        www.mee-t.com);    -   a zinc electrode (12), having Ca 5 mm thickness and 5.5 Ah        nominal capacity, prepared for example as described in PCT        Application PCT/AM2010/000001;    -   a nickel-oxide electrode (13) possessing 1.1 Ah nominal capacity        such as one from NKBN 11 D Ni—Cd accumulator of Lugansk        accumulator production plant; all these electrodes having the        same visible surface area of 40×80 mm²;

2—a porous separator (14) and (15) according to the invention (with DSS)used to wrap the Zinc electrode. The zinc anode, the separator, thecounter electrode and the air-electrode are bathing, immersed in astrong 6M KOH electrolyte.

This battery setup is submitted to cycles of 8 hours 20 mA/cm² chargingand 6 hours discharging at 25 mA/cm².

At first, a battery comprising the separator as described in Example 2is carried out and no dendrite is piercing it after 50 cycles.

Secondly, a battery comprising the separator used is the initial PVCmicroporous separator of example 2, but without the preparationaccording to this invention (i.e. without DSS) is carried out. When usedwithout DSS this separator is pierced by dendrites after less than 5cycles at the same charge-discharge conditions. This example shows thatthe separator of Example 2 possesses enhanced counter-dendritesproperties.

Specific embodiments of the invention have been described by the way ofexemplary teachings however the scope of the present invention is notlimited to the specific details and the illustrative examples shown anddescribed. It will be apparent to persons skilled in the art thatmodifications and variations can be made without departing from thescope of the invention.

The invention claimed is:
 1. A separator which is permeable to hydroxideion, for use in an electrically rechargeable electrochemical cell withalkaline electrolyte between a Zinc electrode and a counter electrode,wherein: said separator consisting in a porous or fibrous materialdefining cavities or pores, wherein said cavities or pores containingwithin at least one Dendrite Stopping Substance or DSS, the said DSSoccupying from 5 to 50% of the volume of said cavities or pores, saidDSS being a metal-containing compound, said metal chosen from the metalsof the group consisting of Pt, Pd, Ni, Fe and Mn metal, and, said DSSbeing in a form of particles and being disposed solely within saidcavities or pores.
 2. The separator according to claim 1 wherein saidDSS is Ni(OH)₂ or one of its precursors.
 3. The separator according toclaim 2, wherein said one of the precursors of Ni(OH)₂ is NiCO₃ orNiSO₄.
 4. The separator according to claim 1, wherein the size of theDSS particles is a positive value below 250 μm.
 5. The separatoraccording to claim 1, wherein the thickness of the separator is from 50to 1000 μm.
 6. An electrically rechargeable battery, with strongalkaline electrolyte, comprising at least one separator according toclaim 1, said separator being placed between a Zinc electrode and acounter electrode.
 7. The electrically rechargeable battery according toclaim 6 comprising an air electrode as a cathode.
 8. The electricallyrechargeable battery according to claim 6, comprising a nickel-oxide orsilver electrode as a cathode.
 9. An electric or hybrid vehiclecomprising at least one electrically rechargeable battery as defined inclaim 6.